The present invention generally relates to locking mechanisms, and more particularly to a fail-safe locking device for reel carrying systems.
Frequently, machines of various types receive or operate on a workpiece. In such machines, it is normally imperative that the workpiece be securely maintained in a desired position, both for purposes for safety as well as efficient operation. One particular case in point involves wire stranders which manufacture stranded cable from a plurality of wires. Some illustrative stranders are described in the following U.S. Pat. Nos.: 2,499,246; 2,958,994 and 3,026,062. In one type of wire strander, known as a tubular strander, the bobbins are placed in cradles which are mounted on bearings in a tubular rotatable frame or housing. During operation, the frame rotates while the cradle and the bobbins or reels are stationary. The wires are paid-out or pulled from the bobbins and are brought along the frame through guides until they are wound on the core wire which is usually taken from a bobbin mounted outside the frame and passed through the frame along a path that is parallel to the axis of the machine, but displaced from the center as are the other wires paid-out from the bobbins loaded on the cradles inside the tubular frame. Such tubular stranders, as well as rigid stranders and planetary stranders are shown and described in the products catalog issued by Ceeco Machinery Manufacturing Ltd. of Ontario, Canada.
A reel supporting unit for a cable stranding machine is described in U.S. Pat. No. 2,958,178. In the aforementioned patent, a pintle assembly is actuatable for axial movements to engage or release a reel. A compression spring is provided within the pintle assembly which acts to cause disengagement between the pintles and the reel, air pressure being supplied to overcome the forces of the spring when engagement of the reel is desired. However, the unit under discussion does not provide fail-safe locking means and failure of the air pressure system releases the reel, this being a major disadvantage and safety hazard, for reasons which will now be discussed.
Since stranders are usually operating at high speeds, and in view of the large rotating masses, a large amount of kinetic energy comes into play. As suggested above, safety hazards involved in operating such machines are considerable. For this reason, safety devices have been developed which normally do not allow the operator to start the machines if any malfunction exists. However, due to failures in the safety systems, as well as due to the pressures of production, there have been numerous instances of accidents which have caused considerable injury to personnel and damage to property.
A major problem with prior art safety devices is that they normally require an operator to perform a number of steps which are time-consuming and, therefore, such systems are inconvenient and reduce production. As a result of this, cases are known where operators have intentionally failed to take the necessary or precautionary steps which ensure the safety of operation of the machine. Accordingly, operators cannot always be depended upon to carry out the loading operation as prescribed for a safe running of the machine, especially when such safety procedures reduce the output of the machines, and therefore, may limit the incentive compensation of the operator. Instances are even known where electrical and mechanical safety systems have been overridden or intentionally bypassed by operators when such systems prevented the operation of a seemingly sound machine.
The safety problem is particularly severe in the case of tubular stranders since the speeds and the energies involved are very high. With respect to such tubular stranders, for example, there are basically three possibilities or types of accidents which can take place. In the first case, the bobbins or reels are not locked properly into position and are released during operation. This jams the reels between the rotatable frame and the cradle causing the cradle to rotate. The reels are eventually thrown out of the tubular frame through the opening thereof. Depending upon the direction of exit, the damage can vary. If the reel is ejected upwardly, it can penetrate through the roof of the building causing injury to persons or damage to property. On the other hand, it can be ejected sideways, thus increasing the chances of injuries to personnel as well as damage to adjacent machines that can, in turn, trigger further accidents. If the bobbin is ejected downwardly, it usually jams the tubular frame against the floor and shatters the tube. Accidents of this type are frequent and heavy damage to property and people have been recorded.
A second type of accident involving tubular stranders can be triggered by a bearing failure which causes the cradle to rotate together with the frame. The consequences of such failure are usually the same since cradles and locking mechanisms are currently designed for stationary conditions and cannot withstand the forces generated when the cradle and the bobbin are rotating at approximately the same speed as that of the tubular frame. The consequence of this situation is a release of the reel and a type of accident similar to that described above. The third type of accident which is possible is that wire gets tangled up around the cradle causing the cradle to rotate and resulting in an accident as above described.
Accidents caused by accidental release of reels have also been recorded in the operation of rigid stranders and planetary stranders, but due to the lower operational speeds, serious damage is less frequent. Furthermore, the open construction of these machines gives the operator a better opportunity to see if a dangerous situation is developing.
Similar problems such as those discussed in connection with above stranders can take place in other types of machinery, particulary where rotatable parts or devices are intended to be temporarily and securely retained on a machine. For example, on those rigid stranders where reels are mounted on cantilevered shafts, operator dependant locking devices are presently used for securing the reels on the shafts. Accidents have been recorded where reel have separated from the shafts on which they are mounted as a result of operator failure to properly secure the manual locking devices. Frequently, when the parts are held, such as by pintles, the positional instability of the pintles is at least partly caused by the high speeds of rotation and the centrifugal forces which are generated thereby. Accordingly, such pintles must not deviate from their retaining positions irrespective of operator negligence and substantially independently of mechanical or electrical failure. Although ball locking devices have been used before, for example, on rewinding machines manufactured by Ceeco Machinery Manufacturing Ltd., and pneumatic-operated spring pintle assemblies are used on tubular stranders manufactured, for example, by the Stolberger Maschinenfabrik & Co. KG of Aachen, West Germany, there is not presently known a fail-safe device for reel carrying systems.
In the following U.S. Patents, some further attempts at providing fail-safe operation in reel supporting machines are described: U.S. Pat. Nos. 2,773,344; 2,787,884; 2,860,479; 2,987,870; and 3,147,702. Generally, the devices disclosed are complex in construction and do not provide the safety margin contemplated by the present invention. For example, the reel supporting devices disclosed in U.S. Pat. Nos. 2,787,884 and 2,860,479 utilize tie bolts which pass through the reel being supported as well as through the pintle members. The tie bolts are either provided with head members or threaded ends for engagement with suitable retaining members which serve to draw the pintle assemblies together into engagement with the supply reel. While the tie bolts can prevent separation of the pintles and release of the reel under normal circumstances, separation of the threaded tie bolt ends from the mating or cooperating members could cause reel release. In any event, the systems described require operator input and, for this reason, suffer the same disadvantages described above. In U.S. Pat. No. 3,147,702, there is disclosed a roll supporting arrangement for a printing press which uses a fluid pressure cylinder biased to release the supported roll, air pressure being used to maintain engagement with the roll. An externally mounted latch is provided to prevent accidental release in the event of air pressure loss. The last mentioned device does not relate to stranding machines and a pivotally mounted latch would not normally be suitable with heavy machinery such as stranding machines. Additionally, the latch of the patent does not act directly on the printing press roll engaging member and this further reduces the reliability of the device to avoid failure. Finally, the device being described requires manual release of the latch to move the cylinder, and the fluid pressure system which actuates the press roll supporting member does not cooperate with the latch. For the aforementioned reasons, the prior art reel supporting systems do not provide the margin of safety, the ease and simplicity of operation, and the minimal amount of operator input which are characteristic of the present invention.